Respiratory Failure Definition: Clinically respiratory failure is defined as PaO2 <60 mmHg while breathing air, or a PaCO2 >50 mmHg. Type 1 respiratory failure - low PaO2 & low or normal PaCO2. -Type 2 respiratory failure -low PaO2 & raised PaCO2 _TYPES OF RF:_ 1. Acute hypoxia without hypercapnia - acute type 1. 2. Chronic hypoxia without hypercapnia - chronic type 1. 3. Acute hypoxia with hypercapnia - acute type 2. 4. Chronic hypoxia with hypercapnia -chronic type 2. Clinical Features: -Cyanosis -Unoxygenated hemoglobin 50 mg/L -Dyspnea: secondary to hypercapnia and hypoxemia -Paradoxical breathing -Confusion, somnolence and coma -Convulsions -Circulatory changes: tachycardia, hypertension, hypotension -Polycythemia: chronic hypoxemia-erythropoietin synthesis -Pulmonary hypertension: Cor-pulmonale or right ventricular failure. ACUTE TYPE 1 RF: _Causes_: -pneumonia. -pulmonary edema. -acute respiratory distress syndrome. -pulmonary embolism. - pneumothorax. _Management:_ -Treat underlying condition. -High conc of oxygen. -Artificial ventilation. CHRONIC TYPE 1 FAILURE: _Causes:_ -diseases associated with pulmonary fibrosis. -chronic chest wall or neuromuscular diseases. -chronic pulmomary edema pulmonary thromboembolism. _Management:_ -Treat underlying cause. -Oxygen therapy. -Artificial ventilation. -Venesection to reduce haematocrit for polycythemic. -Diuretics to reduce peripheral edema. ACUTE TYPE 2 RF: -Causes:_ -depressant drugs like diazepam, opiates & alcohol. -brainstem damage from stroke & trauma. -disorders of nerves & neuromuscular transmission like GBS. -Disorders of muscles like acute polymyositis. -severe airflow obstruction. -chest injuries resulting in tension pneumothorax-flial chest. _Management:_ -treat underlying condition. -oxygen therapy 24% oxygen. -removal of secretions by coughing or emergency bronchoscopic aspirations. -bronchodilators. -assisted ventilation.   CHRONIC TYPE 2 PF: _Causes:_ -COPD. -Chestwall abnormalities like gross kyphoscoliosis. -central hypoventilation. _Management:_ -treat underlying cause. -oxygen therapy carries the risk of rise in PaCO2 resulting in confusion, drowsiness. -measure ABG levels before oxygen therapy. -do not give more than 24% oxygen. -give oxygen continously not intermittently at a rate of 1-2 litre/min. -stimulant drugs advocated like doxapram hydrochloride. -mechanical ventilation reserved for non respondant. -supportive treat includes antibiotics, nebulisers,clearing secretions by coughing, suction. Mechanical Ventilation (MV): -Non invasive with a mask. -Invasive with an endobronchial tube. -MV can be volume or pressure cycled                             -For hypercapnia: •MV increases alveolar ventilation and lowers PaCO2, corrects pH. •Rests fatigues respiratory muscles. -For hypoxemia: •O2 therapy alone does not correct hypoxemia caused by shunt. •Most common cause of shunt is fluid filled or collapsed alveoli (Pulmonary edema). Positive End Expiratory Pressure: -PEEP increases the end expiratory lung volume (FRC). -PEEP recruits collapsed alveoli and prevents recollapse. -FRC increases, therefore lung becomes more compliant. -Reversal of atelectasis diminishes intrapulmonary shunt. -Excessive PEEP has adverse effects •decreased cardiac output •barotrauma (pneumothorax, pneumomediastinum) •increased physiologic dead space •increased work of breathing